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Individual study: Translocation of wild-caught and captive-reared tuatara Sphenodon guntheri to Titi Island, Marlborough, New Zealand

Published source details

Nelson J. N., Keall S. N., Brown D. & Daugherty C. H. (2002) Establishing a new wild population of tuatara (Sphenodon guntheri). Conservation Biology, 16, 887-894

Summary

The tuatara Sphenodon guntheri is a threatened lizard, endemic to New Zealand, occurring only on offshore islands off the main North and South Islands. The tuatara is a long-lived, egg-laying species. It has seen large declines in population size and range, resulting in less than 0.05% occupancy of their original distribution. Population declines and local extinctions on some islands have occurred, and can largely be attributed to the introduction of predators such as rats Rattus spp., dogs Canis familiaris, cats Felis catus and stoats Mustela erminea. Several translocations of tuatara in New Zealand have been carried out although success in terms of establishment of long-term self-sustaining populations are difficult to determine due to their longevity.

Around 300 tuatara occur on North Brother Island in Cook Straight. In 1989, as part of a recovery programme with the aim of establishing two new wild tuatara populations, a captive-rearing programme was established at Victoria University, Wellington. Eggs were also collected from wild populations, and hatched and reared in captivity, in order to reduce demand on adults for translocation purposes. This study describes a translocation to Titi Island using these captive-reared individuals, plus some wild-caught adults.

Release site: Titi Island located in the outer Pelorus Sound (New Zealand), was chosen as a suitable release locality for the captive-reared tuatara. This island was selected due the absence of predators such as brown rat Rattus norvegicus, which were eradicated between 1970 and 1975. Known food sources for tuatara, such as Mimopeus beetles and sea bird eggs and chicks are abundant on the island. Previous studies of tuatara indicate a preference for sunny, north-facing coastal forests, with areas of open vegetation, moderate slopes and sea-bird burrows. Baring these habitat preferences in mind, the release sites were positioned adjacent to the steep north-facing side of the island, containing patches of bare ground and sea bird burrows (affording refugia for the lizards).

Captive rearing: A total of 18 adults (11 females and seven males) were collected for translocation from the tuatara population on North Brother Island. Fifty juveniles ranging in age from three to five years, were selected from those hatched and reared from eggs harvested from the wild population between 1989 and 1991. Selection criteria aimed to ensure maximum genetic diversity. As sex is determined by incubation temperature, harvested eggs were incubated along a gradient of temperature, and juveniles were selected from the entire temperature range in order to ensure that both males and females were translocated (young individuals are difficult to sex). Weight and length were recorded for all individuals. Prior to release, all were toe-clipped to facilitate identification.

Releases: Artificial burrows were installed to provide cover following release. November was chosen as the preferable month for releases, as this is the breeding period and the time of highest activity. Tuatara were transported in damp, well-ventilated cloth bags to Titi Island. Adults were released on 2 November 1995 and juveniles the following day, all between 21:00 and 22:30 hrs, due to their nocturnal nature.

Monitoring: Searches for individuals and observations of breeding behaviour were carried out during six visits following release. A team of 3-4 people spent up to seven nights on the island in survey periods between November 1995 and November 2000. Thorough searches of the artificial burrows and any small burrows in the surrounding area of the release sites were conducted, day and night. Weight and total length were recorded for all re-captured individuals along with snout-vent length measurements for adults.

Re-captures: In total 57% (39/68) of the translocated tuatara were re-captured. Of the adults, 61% (11/18) were re-captured; 56% (28/50) of juveniles were relocated.

From release to the last re-capture, adults had increased in weight by 41%. Adults also showed increases in size; snout-vent length had increased by an average of 18-39 mm five years after release. Approximately two years after translocation, released tuatara were heavier than those from the founder population, on North Brother Island, of the same length. Juvenile weight increased by approximately 100 g (up to 106% increase) in the five years after release.

Breeding activity: The first evidence of breeding activity was apparent when a nest containing six eggs was found in February 1998. However, the eggs showed no signs of embryonic development and were dried out. Despite intensive searches, no other evidence of reproduction was found in the five years post-release.

Conclusions: The translocated tuataras increased in size and weight with approximately 50% survivorship after five years. Evidence of breeding activity (unsuccessful) was recorded. Due to the longevity of the species (tuatara can live to 100 years), a 5-year monitoring period was considered not sufficient a time-scale for the majority of the released individuals to reach sexual maturity (10 to 15 years of age). Therefore future survey visits will be undertaken.

However, the success of the release programme so far is promising, with the head-starting method used for wild-collected eggs and resultant captive-reared juveniles showing increases in weight and size, as well as behavior, matching that of the founder population.


For more information on tuatara see the Department of Conservation (New Zealand) website:

http://www.doc.govt.nz/Conservation/001~Plants-and-Animals/001~Native-Animals/Tuatara.asp


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/doi/full/10.1046/j.1523-1739.2002.00381.x